Organic carboxylic acids are generally known to have antimicrobial properties. Recent work has shown synergistic effect between organic carboxylic acids and other types of antimicrobial agent, such as hops acid. For example, US application 2004/0175480 described that the hops beta acids were more effective as antimicrobial agent if they were in combination with food grade acid, such as lactic acid, acetic acid, propionic acid, citric acid, a potassium ion source, and an antioxidant.
Antimicrobial organic acids are generally soluble in water at high concentration, but some of the organic acid antimicrobial agents are not soluble in water or salted out in the presence of electrolyte. As an example, hops acids are known to have limited solubility in water and the antimicrobial compositions of hops acids described in prior arts are low in active even with the use of organic solvents such as glycols or suspension agents.
One way to combine the different antimicrobial is to spray the liquid antimicrobial agent onto the powdery organic acid or salt, but the resulting composition is not easily dispersible in water. Although wetting or/and emulsifying agents can be formulated into the solid composition, it is more convenient to have liquid products with high active content for handling and use. Products with high active content also save cost in processing, transportation and storage from the sustainability point of view.
It is known that surfactant can help solubilize hydrophobic material in water. Surfactants such as those described in U.S. Pat. Nos. 5,374,614, 7,655,613 and 7,846,889 were utilized to form microemulsions, a thermodynamically stable isotropic liquid, from water-soluble and water-insoluble ingredients. Such microemulsion compositions containing organic acids were also described in U.S. Pat. Nos. 5,294,364, 6,251,844, 7,030,070 and 7,642,227 as acidic cleaning liquids. The organic acid content is low and surfactants used might be prohibited from applications in food or articles in contact with food.
It is desirable to have a single product with all synergistic antimicrobial components in a stable concentrated form with water as the solvent. It is much preferred that the antimicrobial product is of little concern in terms of flammability, corrosivity, toxicity and regulatory requirements.